We are studying primarily yeast enolase and human erythrocyte pyruvate kinase. Enolase work is centered around studying the ligands of the activating and inhibitory metal ions by oxidation of Co ions in situ. ESR, magnetic susceptibility and amino acid analysis will be used to study the oxidation state of the metal and possible oxidation of specific amino acids. Pyruvate kinase work centers on susceptibility to oxidation of sulfhydryl groups and the effect of the oxidation on enzymic activity. The rate of oxidative inactivation of the enzyme is very sensitive to concentrations of affectors and substrates. We will continue this study to define the changes that take place in the enzyme activity within the boundaries of known metabolic changes in the human red blood cell.